Russian and Syrian government forces have launched a new wave of air strikes, killing at least 45 civilians in a besieged area just outside the capital, according to activists.

The onslaught around Damascus came a day after a rash of air strikes battered opposition areas, killing more than 28 people around the country and striking at hospitals and residential buildings in north-western Idlib province.

Syrian government forces have been on the offensive in Idlib in recent weeks but the push intensified after militants shot down a Russian Su-25 fighter jet near the town of Saraqeb over the weekend.

Moscow has waged a punishing aerial campaign against Syria’s armed opposition since intervening in the civil war on the side of its ally, President Bashar Assad, in 2015.

The Britain-based Syrian Observatory for Human Rights said 10 towns in the eastern Ghouta region outside Damascus were bombed on Tuesday. The activist-run Ghouta Media Centre said at least two, Douma and Harasta, was struck by ground-to-ground missiles.

The Syrian Civil Defence search-and-rescue group, known as the White Helmets, which works in opposition areas, called it “another bloody day for civilians” in eastern Ghouta.

It released a video showing its workers rushing to rescue victims from under the rubble. The Observatory said 47 people had been killed, while the Civil Defence put the death toll at 45.

Meanwhile, the lead investigator of a UN-mandated Commission of Inquiry on Syria said his team was looking into reports that bombs allegedly containing weaponised chlorine were used on two recent occasions, in the town of Saraqeb in Idlib, and Douma in Eastern Ghouta.

Paulo Pinheiro, in a statement, added that the spiralling violence in Syria had made “a mockery of the so-called ‘de-escalation zones'” — an agreement last year between Russia, Iran, and Turkey to stabilise the lines of conflict and open corridors for urgently needed humanitarian relief.

He described the government’s siege and indiscriminate bombardment of eastern Ghouta as “international crimes”.